1. Technical Field
The following description relates to a liquid crystal display (LCD) device with a gap spacer for maintaining the cell gap at normal condition and a push spacer (or, Knocking spacer) for maintaining the cell gap when the device is pushed, and method of fabricating the same. Furthermore, the following description relates to a liquid crystal display including a first substrate including a thin film transistor and a color filter, and a second substrate including a gap spacer and a push spacer.
2. Discussion of the Related Art
A liquid crystal display (LCD) device represents video data by controlling the light transmissivity of the liquid crystal layer using the electric fields. According to the direction of the electric field, the LCD can be classified in the two major types: a vertical electric field type and a horizontal electric field type.
For the vertical electric field type LCD, the common electrode formed on the upper substrate and the pixel electrode formed on the lower substrate face each other to form the electric field having a direction perpendicular to the substrate face. The twisted nematic (TN) liquid crystal layer disposed between the upper substrate and the lower substrate is driven by the vertical electric field. The vertical electric field type LCD has an advantage of a higher aperture ratio, while it has a disadvantage of a narrower view angle of about 90° (degrees).
For the horizontal electric field type LCD, the common electrode and the pixel electrode are formed on the same substrate in parallel. The liquid crystal layer disposed between the upper substrate and the lower substrate is driven in an In-Plane-Switching (IPS) mode by the electric field that is parallel to the substrate face. The horizontal electric field type LCD has an advantage of a wider view angle over 160° (degrees) and a faster response speed than the vertical electric field type LCD. Because it often displays a better quality image, the horizontal electric field type LCD is more popular in the market.
Hereinafter, the horizontal electric field type LCD will be explained. The horizontal electric field type liquid crystal display according to the related art comprises a thin film transistor (or, TFT) array substrate, a color filter array substrate, and a liquid crystal layer inserted between these two substrates. FIG. 1 is a plane view illustrating a thin film transistor substrate of the horizontal electric field type liquid crystal display according to the related art.
In the horizontal electric field type liquid crystal display having a thin film transistor substrate, as the pixel electrode and the common electrode are disposed apart from each other with certain distance on the same leveled plane, the video data can be represented by driving the liquid crystal using the horizontal electric field formed between these electrodes. With reference to FIG. 1, the thin film transistor substrate of the horizontal electric field type LCD panel includes a gate line GL and a data line DL crossing each other on a lower substrate, a thin film transistor T formed at the crossing portion of the gate line GL and the data line DL, a pixel electrode PXL and a common electrode COM formed within a pixel area defined by the crossing structure of the gate line GL and the data line DL to form a horizontal electric field, and a common line CL connecting to the common electrode and running parallel with the gate line GL.
The gate line GL supplies the gate signal to the gate electrode G of the thin film transistor T. The data line DL supplies the pixel signal to the pixel electrode PXL through the drain electrode D of the thin film transistor T. The gate line GL and the data line DL are formed in the crossed structure to define the pixel area. The common line CL is formed to be parallel to the gate line GL at one side of the pixel area, and supplies the reference voltage signal for driving the liquid crystal layer to the common electrode.
The thin film transistor T charges and maintains the pixel signal voltage to the pixel electrode PXL by responding to the gate signal of the gate line GL. To do so, the thin film transistor T includes a gate electrode G connected to the gate line GL, a source electrode S connected to the data line DL, and a drain electrode D connected to the pixel electrode PXL. Further, the thin film transistor T may include an active channel layer (not shown) between the source electrode S and the drain electrode D, and an ohmic contact layer (not shown) for keeping the ohmic contact with the source electrode S and the drain electrode D.
The pixel electrode PXL is formed within the pixel area to be connected to the drain electrode D of the thin film transistor T, and exposed via a drain contact hole DH formed through the passivation layer (not shown). Especially, the pixel electrode PXL includes a horizontal pixel electrode PXLh connected to the drain electrode D and is parallel to the neighboring gate line GL, and a plurality of vertical pixel electrodes PXLv branched from the horizontal pixel electrode PXLh that extend in the vertical direction within the pixel area.
The common electrode is connected to the common line CL via a common contact hole CH formed through the gate insulating layer, the passivation layer, and the planarization layer. Some portions of the common electrode that are parallel with the gate line GL having wider width may be a horizontal common electrode COMh. Further, the common electrode includes a plurality of vertical common electrode COMv branched from the horizontal common electrode COMh and extended in the vertical direction within the pixel area. Especially, the vertical pixel electrode PXLv and the vertical common electrode COMv are disposed in parallel with each other within the pixel area.
Therefore, the horizontal electric field is formed between the vertical pixel electrode PXLv supplied with the pixel signal voltage through the thin film transistor T and the vertical common electrode COMv supplied with the reference signal voltage through the common line CL. Due to this horizontal electric field, the liquid crystal molecules of the liquid crystal layer disposed between the thin film transistor array substrate and the color filter substrate are rotated by the dielectric anisotropy. Based on the rotating amount, the light transmittance of the pixel area is altered, and then the video image can be represented.
The thin film transistor substrate is joined with the color filter substrate with the liquid crystal layer therebetween. Here, in order to keep the gap between the thin film transistor substrate and the color filter substrate uniform, a plurality of gap column spacer GCS may be disposed on the inner surface of the color filter substrate. The gap column spacer GCS may be formed to overlap with the non-open area (to not allow the light to pass) where the lines and/or the thin film transistor is formed.
On the overall area of the liquid crystal display, the gap column spacers GSC would be disposed as being scattered with a proper distribution density. FIG. 2 is a plane view illustrating a distribution of the gap column spacers in the liquid crystal display according to the related art. With reference to FIG. 2, the liquid crystal display includes a plurality of unit pixels disposed in a matrix manner, where each unit pixel has a group of subpixels including a red subpixel, a green subpixel, and a blue subpixel. For example, the red color filters CFR allocated at red subpixels may be disposed along one column, and the green color filters CFG may be disposed along the next column. Further, the blue color filters CFB may be disposed along the next column after the green color filters CFG.
With this pixel array structure, the liquid crystal layer is sandwiched between the thin film transistor substrate and the color filter substrate. A plurality of the gap column spacers GCS are distributed with the liquid crystal layer for maintaining the thickness of the liquid crystal layer (i.e., Cell Gap) in even or uniform condition. FIG. 2 shows an example distribution of the gap column spacers in which four (4) gap column spacers are evenly distributed within a 25×9 pixel array.
Due to the gap column spacer GCS, the thickness between the thin film transistor substrate and the color filter substrate can be maintained in an even and/or uniform condition. However, when a touch panel has been applied to the liquid crystal display, a user may frequently press the surface of the liquid crystal display. In this case, at the area where there is no gap column spacer GCS, the cell gap may not be maintained in uniform condition due to the pressing force of the user's finger (the “touch pressure”). As this touch pressure is not always the same, the cell gap may be severely thinned when the user touches the display surface with a strong pressing force. When these touches are frequently repeated, the display quality may have any unexpected problem or may be damaged.
Therefore, with the exception of the gap spacer for keeping the cell gap in uniform condition, it is desirable to have a means or structure to prevent the cell gap from being severely thinned when the user presses/touches the display surface.